Most polymeric solutions demonstrate non-Newtonian flow and a measurement of viscosity and first normal stress difference typically requires expensive and cumbersome equipment. Commercially available equipment includes cone and plate-type shear rheometers to measure both the viscosity and first normal stress difference of a polymeric solution. In a cone and plate-type shear rheometer, a small quantity of fluid is sheared between a cone and rotating plate and the normal and tangential forces exerted on the plate are measured and used to deduce the first normal stress difference and viscosity, respectively. However, the cone and plate-type shear rheometers suffer from several drawbacks. The cone and plate rheometers are expensive and of considerable size, thus detracting from their usefulness and availability.
In addition, due to the size of cone and plate rheometers, the measurement of the first normal stress difference and viscosity with respect to toxic fluids exhibiting non-Newtonian flow is not desirable and in some instances dangerous since such rheometers cannot fit into a conventional size glovebox. Since the fluid often spins out from the plate as it is rotated at high revolutions, its use and application to the measurement of viscosity and first normal stress difference with toxic fluids is limited, and in some cases is to be avoided.
A variety of other instruments are available for the measurement of viscosity of polymeric fluids, however, no method has yet been developed to permit these instruments to measure the first normal stress difference and there is no corollary yet available to equate the data derived from these instruments with existing data to determine the first normal stress difference.